Iodine avidity in papillary and poorly differentiated thyroid cancer is predicted by immunohistochemical and molecular work-up.

Background: Successful radioiodine treatment of differentiated thyroid cancer requires iodine avidity: that is, the concentration and retention of iodine in cancer tissue. Several parameters have previously been linked with lower iodine avidity. However, a comprehensive analysis of which factors best predict iodine avidity status, and the magnitude of their impact, is lacking.

Methods: Quantitative measurements of iodine avidity in surgical specimens (primary tumour and lymph node metastases) of 28 patients were compared to immunohistochemical expression of the thyroid-stimulating hormone receptor, thyroid peroxidase (TPO), pendrin, sodium-iodide symporter (NIS) and mutational status of BRAF and the TERT promoter. Regression analysis was used to identify independent predictors of poor iodine avidity.

Results: Mutations in BRAF and the TERT promoter were significantly associated with lower iodine avidity for lymph node metastases (18-fold and 10-fold, respectively). Membranous NIS localisation was found only in two cases but was significantly associated with high iodine avidity. TPO expression was significantly correlated with iodine avidity (r = 0.44). The multivariable modelling showed that tumour tissue localisation (primary tumour or lymph node metastasis), histological subtype, TPO and NIS expression and TERT promoter mutation were each independent predictors of iodine avidity that could explain 68% of the observed variation of iodine avidity.

Conclusions: A model based on histological subtype, TPO and NIS expression and TERT promoter mutation, all evaluated on initial surgical material, can predict iodine avidity in thyroid cancer tissue ahead of treatment. This could inform early adaptation with respect to expected treatment effect.